gguf : remove is_lora from Model class

I must have added this back by mistake when rebasing.

convert_hf_to_gguf.py

@@ -102,7 +102,6 @@ def __init__(self, dir_model: Path, ftype: gguf.LlamaFileType, fname_out: Path,
         self.metadata_override = metadata_override
         self.model_name = model_name
         self.dir_model_card = dir_model  # overridden in convert_lora_to_gguf.py
-        self.is_lora = is_lora  # true if model is used inside convert_lora_to_gguf.py
         self.preprocessor_config = self.load_preprocessor_config(self.dir_model)
 
         # Apply heuristics to figure out typical tensor encoding based on first layer tensor encoding type